This invention relates to positioning fixtures useful with measuring platens in systems using radiation techniques for measurement of ultra thin coatings and the like, and particularly beta backscatter measuring systems such as described, for example, in U.S. Pat. No. 3,132,248 dated May 5, 1964.
In such systems it is important that the component area being measured be carefully delimited, and for that purpose it is known to provide interchangeable platens having exposure apertures of different sizes and configurations, thereby permitting the system to be used with an aperture best suited to the component being measured. Such interchangeable platens are shown, for example, in U.S. Pat. No. 3,115,577 dated Dec. 24, 1963.
Even with appropriately shaped and sized apertures, the positioning of small parts can be difficult and time consuming, particularly where repeatability in positioning is important. It is known to provide a fixture which is shaped to receive a particular part, for use with the aperture plate or platen to facilitate the positioning of successive identical parts. To measure a differently shaped or sized part, a different positioning fixture is provided. This requires a multiplicity of fixtures.